He’d done anti-methamphetamine campaigns before. But staying away from meth is an easier sell: Show some busted teeth, some pockmarked skin, no sweat.

How do you encourage kids not to use marijuana at a time when acceptance of pot is at historic highs and Colorado is more awash in conflicting marijuana messages than any place in the country?

“This was a tricky one,” Sukle said.

The result launches Monday, when workers begin dropping human-size rat cages around Denver and ads that acknowledge debate about how dangerous marijuana is begin running on television and in movie theaters.

The campaign is called “Don’t Be a Lab Rat.” The idea is to suggest to kids that Colorado has become a testing ground on the consequences of marijuana legalization — and they will be the test subjects if they use pot.

Sukle said the goal isn’t to scare kids with the usual claims about what will happen to them if they use marijuana. Instead, it’s to unsettle them with the uncertainty that they can’t be sure what will happen.

“We don’t say, ‘It’s absolute’; we say, ‘This study exists. Some people dispute that. Make up your own mind,’ ” Sukle said. “At some point, they have to make up their mind. The days of Just Say No, that was a fairly failed effort.”

Crafting a message to dissuade kids from using drugs always has been a tightrope walk, and the history of such campaigns is mostly marked by failure.

The DARE campaign, a staple in classrooms two decades ago, has been shown innumerousstudies to have had little impact on teen drug use. A study published last year revealed that when parents try to discourage their kids from using drugs by talking about their own youthful experimentation, kids are less likely to perceive drug use as harmful. A study from 2005 showed that anti-drug ads often backfire and instead prompt experimental curiosity in kids, in part because they cause kids to think that everybody else is already doing drugs.

What many of the campaigns shared was a theme: Fear. But Ohio State University professor Michael Slater, an expert on drug-prevention campaigns, said trying to scare kids away from marijuana usually isn’t effective because many teens see themselves as risk-takers. Telling that group to be afraid comes across more like a challenge.

“Those kids are more likely to experiment with drug use,” Slater said.

One campaign Slater found to be effective used that dynamic to its benefit. The nationwide “Above the Influence” campaign, which began in 2005, portrayed marijuana use as stifling — and told kids to be rebels.

“As long as it’s seen as a way to rebel and feel independent, kids will explore that,” Slater said.

Conscious of the graveyard of previous anti-marijuana campaigns, Sukle and his team built the “Lab Rat” campaign from ground up. They started by recruiting kids to hang out with friends in places familiar to them — their homes, for instance, or a recreation center — and talk about marijuana.

In those hangouts, the ad folks pitched some possible messages. Marijuana could cost you a scholarship was one. Marijuana could land you in trouble was another. But none of those messages stuck, Sukle said.

There was some brief discussion about using celebrities in ads. But internal e-mails suggest that Sukle’s agency wasn’t thrilled with the idea of using one spokesman that Gov. John Hickenlooper has publicly suggested: 81-year-old country music star and noted marijuana enthusiast Willie Nelson. Will many kids even know who he is, the ad folks asked?

“If we’re going to talk to kids, we need to be sure the message — and the messenger — will resonate,” a member of Sukle’s team wrote, as quoted in an e-mail from a Hickenlooper staffer that was obtained through an open-records request.

Ultimately, Sukle decided, the ads needed to hit on something personal: The kids’ sense of self. When teens were told about research that suggests marijuana could affect developing brains, it bothered them.

“Their brain makes them who they are,” Sukle said. “Their brain is the key to opening up all those experiences down the road.”

Teens, naturally, also didn’t like the idea of being watched. “Don’t Be A Lab Rat” was born.

The project will cost about $2 million, much of which comes from a grant from the state attorney general’s office that itself comes from legal settlements with various pharmaceutical companies, according to the governor’s office.

The campaign will feature a handful of human-size rat cages — complete with attached giant water bottles — scattered throughout the city and festooned with posters bearing the campaign’s messaging. One poster, for instance, will read: “Volunteers needed. Must have a developing brain. Must smoke weed. Must not be concerned about schizophrenia.”

The television and movie theater spots have a similar tone. In one, teens are shown lighting up in a smoke-filled car. Text on screen tells of a Duke University study that argued teenage marijuana use causes lasting drops in IQ.

“Some dispute that study,” the text continues. “But what if, years from now, you learn they were right?”

He said the ad campaign sounds like more fear-mongering. Referencing the classic frying-egg ad with the message, “This is your brain on drugs,” Tvert said the “Lab Rat” campaign is basically just a twist: “This is your brain. It could fry.”

“What it comes down to is are the ads intended to scare them or are the ads intended to inform them?” he asked. “These ads are intended to scare them.”

But state officials are hopeful. In a statement last week accompanying the release of a new survey on teen marijuana use in Colorado, state health department head Larry Wolk referenced the campaign. The survey showed that Colorado teens’ perceptions of marijuana’s harmfulness — already among the lowest in the nation — had dropped again, but showed no increase in marijuana use.

“If we want Colorado to be the healthiest state in the nation,” Wolk said, “then we need to make sure our youngest citizens understand the risks of using potentially harmful substances.”